Movable vehicles, such as automobiles, trucks, buses, boats, airplanes, motorcycles and motorized bicycles, are occasionally misplaced, lost or stolen, sometimes permanently. Between one and two percent of the automobiles three years old or less are stolen or taken, and the percentage of recovery of such vehicles is about 63 percent. Several inventors have developed methods that might be used to recover a missing vehicle, by continuous tracking of that vehicle.
A personnel locator system is disclosed in U.S. Pat. No. 3,439,320, issued to Ward. Each person carries a sensor/transmitter that emits a unique frequency whenever that person enters any one of a plurality of selected areas in a facility, with each such area having a receiver that receives this signal and transmits this information to a central processor. The processor keeps track of the movements of each person from one selected area to another area so that, at any given time, the processor can identify the selected area a given person now occupies. This approach is limited to a relatively small geographic area and to a relatively small number of covered persons.
Serrano et al disclose a microprocessor-controlled interface for a cellular phone system to be carried in a vehicle, in U.S. Pat. No. 4,718,080. A telephone handset communicates with the cellular transceiver along a bus and through the microprocessor that interprets bus logic signals, including voice and data signals. No integration is disclosed of the on-board cellular system with any instrument that reports vehicle operating information upon command received from a remote site.
U.S. Pat. No. 4,797,671, issued to Toal et al, discloses a motor vehicle locator system that indicates the location of a parked vehicle within a controlled area, such as a large parking lot. Each parked vehicle carries a receiver and audio/visual signal emitter. The receiver responds only to receipt of a signal having a unique frequency and causes the emitter to emit an audible or visually perceptible signal that indicates the present location of the parked vehicle. This approach requires that the vehicle be located within a controlled area of modest size, probably no larger than a city block.
Ando et al,, in U.S. Pat. No. 4,837,700, disclose method and apparatus for processing and displaying the present location of a road vehicle, using a GPS receiver to provide data on vehicle location. This approach provides continuous information on vehicle location and vehicle orientation or movement vector based upon sensing the Earth's local geomagnetic field direction. An angular rate sensor determines, and optionally displays, the angular rate of change of vehicle orientation, and an odometer determines the distance the vehicle has moved over some predetermined time interval. The present vehicle location can be displayed graphically on an electronic map carried within the vehicle, with a sequence of maps being used to display the changing vehicle location. Map size can also be increased or decreased, and the displayed map can be automatically scrolled as vehicle position changes. A keyboard is available for entering instructions into a controller or processor. A reference location can be entered into the system, and vehicle location can be determined relative to this reference location. The location data can be stored if these data are acceptable and can be dumped into a bit bucket if these data are not acceptable.
In U.S. Pat. No. 4,924,402, Ando et al disclose a more detailed approach for determining and graphically displaying vehicle location using a GPS. This system uses a magnetic field sensor, an angular velocity sensor and a travel distance sensor together with GPS data and stores maps together with numerical data that describe useful features of the local terrain. Sensing of vehicle distance traveled and directional rams made is intended to be sufficiently accurate that the map displays the location of the vehicle relative to road intersections (i.e., approaching, passing through, turning, etc.). With reference to FIGS. 16-17, 22, 27-28 and 30, the invention appears to put a premium on receiving GPS data that are accurate to within one meter.
A paging system with paging request receivers that respond or are controlled differently, depending upon receiver location, is disclosed by Vrijkorte in U.S. Pat. No. 4,943,803. Using "angle modulation" whose operation is not explained, the paging request receiver is said to pick out the strongest transmission control signal from among simultaneously transmitted control signals and to respond to this signal, if the signal received includes the receiver's predetermined address code. The receiver goes into a "sleeper" mode if no signals specifically addressed to that receiver are received within a selected time interval. The receiver is activated for receiving a control message by receipt of a receiver activation signal that may vary with the geographic zone presently occupied by the receiver.
A portable target locator system is disclosed by Ruszkowski in U.S. Pat. No. 4,949,089. The locator uses a laser beam target locator and a GPS. The target locator is aimed by an observer on the ground at a nearby target, such as a moving tank. The position of the target is sensed using a return signal received by the target locator, and the position coordinates are transmitted by a modem to a weapon system, such as an aircraft. The weapon system uses this target position to direct a bomb or whatever to the target. If GPS position information is unavailable, the target position is determined manually. The target locator includes a rifle-like beam director that determines the target location relative to the beam director location and orientation. This information is transmitted to the weapon system, which also senses its own GPS-determined system and determines target position by an approach that may use differential positioning.
Nishikawa et al disclose a land vehicle navigation system in U.S. Pat. No. 4,949,268. A combination of three or more GPS satellites is selected, from among all available GPS satellites, that provides the best vehicle location data. Here, a figure of merit used is minimum position dilution of precision ("PDOP") associated with the data received from a given group of GPS satellites. This approach seeks to account for the possibility that one or more buildings or other structures of relatively great height may preclude satellite visibility. The height of the structures in that area may be stored as part of a map in a GPS processor on board the land vehicle whose location is to be determined. The on-board system seeks combinations with the highest number of satellites visible, then works from these combinations to minimize the PDOP or a similar figure of merit for GPS position data.
Bezin et al disclose a system for managing already-paid vehicle parking fares by means of information cards affixed to the vehicles, in U.S. Pat. No. 4,982,070. The card contains a confidential identification number for the vehicle and the prepaid vehicle parking and includes an adhesive label that allows the card to be affixed to a vehicle windshield or another visible area. A portable card checking machine, carded by a roving parking lot operator, allows readout of this information from the card.
A satellite signal tracking method for signal reacquisition in the presence of a "dead zone", such as a tunnel or very tall adjacent building that interrupts receipt of all GPS signals, is disclosed by Ando in U.S. Pat. No. 4,983,980. The tracking system determines the satellite that had the maximum elevation angle at the moment the GPS signals are interrupted and seeks and m-tracks that satellite as soon as the receiver clears the dead zone. The signal from the satellite with the next highest elevation angle is then reacquired and re-tracked, and so on. This allegedly minimizes the time for signal reacquisition. Little quantitative information is disclosed in this patent.
Scribner et al disclose a vehicle tracking system that records, but does not transmit, the location of a vehicle whenever one or more predetermined events occurs in U.S. Pat. No. 5,014,206. The vehicle carries sensors that respond to occurrence of a predetermined event and carries a GPS or LORAN navigational system that receives vehicle location information, such as longitude and latitude. This vehicle location information is stored in a memory on board the vehicle only when one or more of the predetermined events occurs. The vehicle location information is assumed to be read out periodically when the vehicle returns to a home base.
In U.S. Pat. No. 5,043,736, Damell et al disclose use of a combined cellular telephone and GPS portable receiver system that provides latitude and longitude coordinate information for the receiver. The GPS receiver has a modem and transmitter connected thereto that transmit its position to an accessible cellular phone, which in turn notifies a stationary base unit of the location of the GPS receiver. The base unit graphically displays the present location of the GPS receiver. This patent does not disclose communication with the receiver by a paging system located elsewhere, to activate the transmitter and modem, nor activation of a GPS receiver in a vehicle that is later determined to be missing.
On-board navigation apparatus, to be carded on a vehicle to compare present and immediate-past locations as determined from GPS data, is disclosed by Odagawa et al in U.S. Pat. No. 5,087,919. A map containing coordinates for all roads in a region of the Earth's surface is stored electronically in a navigation system on board the vehicle, as part of a "map" of the region. The navigation system apparently assumes that the vehicle stays on one of the roads. Using the continuously arriving GPS data, the system searches for the nearest road segment that is consistent with these data to determine present location of the vehicle. Only latitude and longitude data are needed here so that fewer than four satellites may be used to determine the present location. Elevation data are provided as part of the road description stored in the navigation system. This system would not work well for a vehicle, such as an off-road land vehicle or a marine vessel, that has no fixed system of roads or paths to follow. This approach would not be particularly useful in determining the location of a stolen vehicle, unless the thief could be relied upon to stay on the conventionally describable roads.
Timothy et al, in U.S. Pat. No. 5,101,356, disclose providing a surface or airborne vehicle with three spaced apart antennas, each connected to a GPS receiver. The receiver output signals are connected to a phase comparator system that compares GPS signal phase differences and determines the vehicle attitude or orientation (pitch, roll and yaw) relative to a fixed spatial frame. Location of the vehicle is not of interest here.
Lojack Corp. of Dedham, Mass. has demonstrated a vehicle location system using triangulation of radio signals transmitted from the vehicle by a large number of receivers that are strategically positioned around a community. The vehicle transmitter is remotely activated by a signal broadcast from elsewhere.
These patents disclose use of GPS or related technology for determination of location or orientation of a person or vehicle continuously or at discrete times, without regard to the associated consumption of power, cost of tracking the vehicle, or cost of communicating the vehicle location. What is needed is a system that allows determination of location of a vehicle only when a trigger event occurs, such as misplacement or theft or unauthorized movement of the vehicle, so that power usage is controllable and is minimized, and communication from and tracking of the vehicle are minimized. The system should allow communication at will between the GPS receiver and an inquirer located elsewhere.